Nitric Oxide Inhalation During Exercise in Chronic Obstructive Pulmonary Disease

Patients with chronic obstructive pulmonary disease (COPD) may develop hypoxemia and pulmonary hypertension when exercising. To investigate whether inhaled nitric oxide (NO), a selective pulmonary vasodilator, modifies the changes induced by exercise in pulmonary hemodynamics and gas exchange in COPD, we studied nine patients (FEV1 = 39 ± 2% predicted), at rest and at submaximal exercise, during breathing of room air and NO (40 ppm). NO inhalation decreased pulmonary artery pressure (Ppa) both at rest and during exercise (analysis of variance [ANOVA] p < 0.05). However, the effect of NO on PaO2 was different at rest than during exercise. At rest, NO decreased PaO2 from 72 ± 3 mm Hg to 65 ± 2 mm Hg, due to an increase in ventilation–perfusion (V˙ a/Q˙) inequality (dispersion of blood flow distribution from 0.9 ± 0.1 to 1.1 ± 0.1). During exercise, PaO2 decreased during breathing of room air ( − 5 ± 3 mm Hg), whereas it remained essentially unchanged during inhalation of NO ( + 2 ± 3 mm Hg), with both chang...